1. Field Of The Invention
This invention pertains, in general, to hand-held cutting tools, and in particular, to an improved, adjustable-blade safety knife and a carton-cutting guide therefor.
2. Description Of The Related Art
Adjustable-blade knives in which a replaceable, single-edge blade having a very sharp cutting edge is slideably-retained within a handle assembly have found widespread use in a variety of industries, for a variety of tasks, e.g., shipping-and-receiving, wallboard construction, wallpapering, tile-laying etc.
Such a useful tool has previously been disclosed in U.S. Pat. No. 4,089,112 to J. L. Richards, and assigned to the instant assignee. This knife has a one-piece, extruded handle in which a continuous, longitudinally-extending recess forms a web between thicker edge portions, the recess extending laterally into the edge portions to form a pair of continuous, longitudinally-extending top and bottom slots, each slot having a pair of oppositely-faced side walls, one of which side walls is adjacent and co-planar to one side wall of the web, between which side walls are slidably-retained the top and bottom edges, respectively, of a keeper-plate-and-cutting blade assembly, the blade having a central aperture and being constrained to slide within the slots in side-by-side relationship with the keeper plate by the engagement of a laterally-extending tang on the top edge of the plate within one of a plurality of notches in the top edge of the blade, the assembly being adjustably-retractable in and out of the forward end of the handle through a plurality of locked positions by movement of a cammed button member acting in cooperation with a spring arm formed integrally of the keeper plate and a notched slot in the web.
As a consequence of its low cost, light weight and safe reliability, the knife has received considerable commercial acceptance, along with suggestions from customers of areas for improvement of it and other such available knives.
One such area concerns the replaceability of the blade. These blades are so-called "all-purpose" or "AP" blades of the type manufactured by, e.g., Americal Safety Razor Co. or Ardell Industries, Inc., and are retained within the handle of the knife at the bottom by the lower groove and at the top by the upper groove and the engagement of a bent-over finger, or tang, which engages one of a plurality of the notches in the upper edge of the blade provided by the manufacturer. The blade is removed from the knife by extending the keeper plate and blade assembly all the way forward out of the knife, which permits the blade to be swung down at its rear, lower end away from its engagement with the tang in the keeper plate. It has been learned that, in some cases, especially when the keeper plate and blade are extended completely forward with some force, the blade will simply drop from the handle by its own weight, resulting in a dropped and/or possibly lost blade. Thus, it would be desirable if means could be provided for retaining the blade on the keeper when both are fully extended from the knife, so that the blade may be manually removed by the user.
Another such area for improvement relates to the method of indexing the blade to the keeper plate within the knife. As discussed above, the blade is so indexed by means of the engagement of the tang on the top of the keeper plate within one of the plurality of notches on the blades's top edge. The tang cannot be made to extend laterally across the complete width of the blade because, for tolerance reasons, the end of the tang might interfere with the side wall of the upper groove adjacent to the blade, resulting in galling or jamming of the knife. It has been learned that, under certain circumstances in which considerable cutting force is being exerted on the blade by the user, particularly forces having components acting laterally to the blade, the blade and/or keeper can be deformed apart to the extent that the tang becomes disengaged from the blade, resulting in dislodgement of the blade from the handle.
Yet another suggested area for improvement in the knife relates to its use for cutting open cardboard cartons by stocking clerks in grocery stores, and the like. Their duties entail the frequent opening of cardboard shipping containers to remove the products therefrom for shelf stocking which typically involves slicing the top of the carton through the side wall of the container with a sharp knife. If the contents of container are not tamped thoroughly and/or the knife is not applied with a steady hand and a keen eye, the valuable contents of the containers can be sliced through and damaged. Accordingly, they have suggested that it would be desirable to provide some means for guiding the knife while cutting open a container which would prevent injury to the container's contents.
A type of cutting guide is described in U.S. Pat. No. 3,195,231 to H. M. Lightburn for "Razor Blade Holder And Accessory Therefor." Unfortunately for the above, Lightburn's holder and accessory are adapted for generating a pair of display trays for the carton contents from the paper shipping cartons, and not to the protection of the contents of the carton during cutting.